Components on integrated circuits can be electrically insulated from one another in order that the components do not mutually influence one another in terms of their functions. In high-voltage applications, in particular, not just individual components but entire functional groups are arranged in a manner electrically insulated from one another. By way of example, in bridge arrangements, switches and driving circuits are constructed in electrically insulated fashion.
Junction-isolated monolithic high-voltage technologies are widespread. They can be used for half-bridge drivers. In the case of a half-bridge driver, part of the circuit is situated within a generally N-conducting region and is insulated from the rest of the circuit by lightly doped PN junctions in the reverse direction.
A signal flow for a high-side driver is effected from the driving circuit in the direction of the driver circuit by means of high-voltage NMOS transistors. The blocking capability of the PN junctions between the driving circuit and the high-voltage NMOS transistors determines the maximum supply voltage of the entire half-bridge circuit. High-voltage ICs of this type can be produced cost-effectively and operate comparatively slowly owing to the structure sizes required for the blocking capability. Customary signal transit times are of the order of magnitude of 500 ns. Furthermore, they are particularly susceptible to electromagnetic influencing owing to the weakly doped P- and N-type regions with long minority carrier lifetimes.
SOI technologies (Silicon on Insulator) are furthermore used, in the case of which a silicon wafer provided with an oxide layer can have a further silicon wafer bonded onto it. One of the two wafers can subsequently be eroded to a thin residual layer. The thin residual layer can have a thickness of a few 100 nm up to a few (m. Individual regions of the residual layer are electrically insulated from one another by means of a patterned etch. Circuit regions that are completely insulated from one another are thus obtained. The production costs are relatively high, and the circuits operate relatively rapidly compared with the structure sizes used. High-voltage NMOS transistors are likewise used for the signal flow, or the level conversion from the driving circuit to the driver circuit.
Furthermore, there is the possibility of providing circuit regions that are to be insulated from one another on separate chips and of mounting the chips into a housing in a manner insulated from one another. The signal transfer can be effected for example by means of air-core coil transformers integrated on a chip and having mutually insulated primary and secondary windings. One feature of this solution is that no special high-voltage technology is required. Since technologies having small structures and high packing density can be used for this purpose, the signal transfer is approximately a factor of 100 faster than by means of junction-isolated high-voltage technologies. The blocking capability of the insulation path is very high and independent of a polarity of the reverse voltage. By way of example, the number of chips increases with the number of half-bridges to be mounted. For a three-phase bridge driver, by way of example, four chips in a housing are required. The housing size and the mounting complexity increase with the number of chips. Monolithically integrated half-bridge drivers can be incorporated into smaller housings than half-bridge drivers having separate chips.
In order to increase the packing density in the case of monolithically integrated power circuits, by way of example, the lateral insulation of the components among one another can be implemented by means of isolation trenches. The isolation trenches require less space than the junction isolation that is otherwise customary. The isolation trenches reach from the chip surface down into a depth at which functional PN junctions no longer occur, that is to say down to a depth of approximately 10 . . . 20 μm. This depth is significantly smaller than the chip thickness.